The present invention relates generally to material dispensing systems for applying material onto a substrate and, more particularly, to a material dispensing system having a modular die assembly for applying in a controlled manner patterns of fibrous material onto a moving substrate.
Various dispensing systems have been used in the past for applying patterns of viscous material onto a moving substrate. In the production of disposable diapers, incontinence pads and similar articles, for example, hot melt adhesive dispensing systems have been developed for applying a laminating or bonding layer of hot melt thermoplastic adhesive between a non-woven fibrous layer and a thin polyethylene backsheet. Typically, the hot melt adhesive dispensing system is mounted above a moving polyethylene backsheet layer and applies a uniform pattern of hot melt adhesive material across the upper surface width of the backsheet substrate. Downstream of the dispensing system, a non-woven layer is laminated to the polyethylene layer through a pressure nip and then further processed into a final usable product.
In one known hot melt adhesive dispensing system, continuous beads or strands of adhesive are emitted from a multiple adhesive outlet die with multiple air jets oriented around the circumference of each material outlet. The multiple air jets drive air tangentially relative to the orientation of the adhesive strand as it emits from the die orifice, thereby attenuating each adhesive strand and causing the strands to swirl before being deposited on the upper surface of the moving substrate.
More recently, manufacturers of diaper products and others have been interested in small fiber technology for the bonding layer of hot melt adhesive in non-woven and polyethylene sheet laminates. To this end, hot melt adhesive dispensing systems have incorporated slot nozzle dies with a pair of angled air channels formed on either side of the elongated extrusion slot of the die. As the hot melt adhesive emits from the extrusion slot as a continuous sheet or curtain, pressurized air is emitted as a pair of curtains from the air channels to impinge upon, attenuate and fiberize the adhesive curtain to form a uniform fibrous web of adhesive on the substrate. Recently, fibrous web adhesive dispensers have incorporated intermittent control of adhesive and air flows to form discrete patterns of fibrous adhesive layers with well defined cut-on and cutoff edges and well defined side edges.
Meltblown technology has also been adapted for use in this area to produce a hot melt adhesive bonding layer having fibers of relatively small diameter. Meltblow dies typically include a series of closely spaced adhesive nozzles that are aligned on a common axis across the die head. A pair of angled air channels are formed on either side of the adhesive nozzles to extend parallel to the common nozzle axis. As hot melt adhesive emits from the series of aligned nozzles, pressurized air is emitted from the air channels as a pair of curtains that impinge upon, draw down and attenuate the fibers before they are applied to the moving substrate.
While meltblown technology has been used to produce fibrous adhesive layers on moving substrates, it has several drawbacks. As those skilled in the art will appreciate, meltblown technology typically uses a high volume of high velocity air to draw down and attenuate the emitted adhesive strands. The high velocity air causes the fibers to oscillate in a plane that is generally aligned with the movement of the substrate, i.e., in the machine direction. To adequately blend adjacent patterns of adhesive to form a uniform layer on the substrate, meltblow dispensers require the nozzles to be closely spaced. Moreover, the volume and velocity of the air must be high enough to sufficiently agitate and blend adjacent fibers.
However, the high volume of air used in meltblown dispensers adds to the overall operational cost as well as reduces the ability to control the pattern of emitted fibers. One byproduct of the high velocity air is xe2x80x9cflyxe2x80x9d in which the fibers get blown away from the desired deposition pattern. The xe2x80x9cflyxe2x80x9d can be deposited either outside the desired edges of the pattern, or even build up on the dispensing equipment which can cause operational problems that require significant maintenance. Another byproduct of the high velocity air and closely spaced nozzles is xe2x80x9cshotxe2x80x9d in which adjacent adhesive fibers become entangled and form globules of adhesive on the backsheet substrate. xe2x80x9cShotxe2x80x9d is undesirable as it can cause heat distortion of the delicate polyethylene backsheet.
It will further be appreciated by those skilled in the art that the construction of the meltblow dies, with the continuous sheets of air formed on either side and parallel to the aligned nozzles, reduces the ability of manufacturers to modularize the meltblow dies in side-by-side fashion across the width of a moving substrate. The curtains of air are interrupted between adjacent melt blow dies which generally results in a less consistent fiber pattern on the substrate.
Additionally, the many closely spaced nozzles required in meltblow dies not only adds to manufacturing costs, but also forces lower material flow rates through each nozzle. Lower material flow rates per nozzle generally results in a greater variation of the fibers emitted from the nozzles. Moreover, the nozzles are typically more likely to clog at the lower material flow rates.
Thus, there is a need for a material dispensing system that improves control of dispensed material to form patterns on a moving substrate without xe2x80x9cflyxe2x80x9d or xe2x80x9cshotxe2x80x9d. There is also a need for a material dispensing system that reduces costs associated with operation and maintenance. There is yet another need for a material dispensing system that improves the ability to modularize the dispensing system to provide a wider range of uniform material pattern widths across a moving substrate.
The present invention overcomes the foregoing and other shortcomings and drawbacks of the material dispensing systems and methods heretofore known. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
The present invention is directed to a material dispensing system and method for use in applying in a controlled manner a fibrous material in a desired pattern on a moving substrate. The material dispensing system has a source of fluid material to be applied and a source of pressurized air that are connected to a material dispensing head. The material dispensing head has a fluid manifold connected to the source of material, an air manifold connected to the source of pressurized air, and a dispensing module having an upper dispensing body and a lower modular die assembly mounted to one end of the dispensing body. The dispensing body is connected to the fluid manifold for delivering fluid in a controlled manner to the die assembly. The modular die assembly includes a series of aligned material outlets that emit the fluid in a series of spaced strands toward a substrate. The dispensing body is connected to the air manifold for delivering pressurized air in a controlled manner to the die assembly. The pressurized air is used to draw down and attenuate the strands to form fibers that oscillate in a generally transverse plane relative to the direction of travel of the moving substrate. The oscillation of the fibers provides a uniform pattern of fibrous material on the moving substrate. The pressurized air between the material outlets also separates the strands during the critical draw down phase to prevent entanglement of adjacent strands. The orientation of the air and material outlets in accordance with the principles of the present invention improves control of the dispensed material to form a desired pattern on the moving substrate.
In accordance with one aspect of the present invention, the modular die assembly has a die block mounted to a lower end of the dispensing body. The die block has a seat for mounting a pattern die and sealing plate to a lower end of the die block. Material passages are formed in the die block for delivering viscous material from the dispensing body to the pattern die. Air passages are also formed in the die block for delivering pressurized air from the air manifold to the pattern die. The sealing block is mounted to provide a seal between the various components of the modular die assembly.
The pattern die has a series of spaced openings that are preferably aligned on a common axis along a lower surface of the pattern die. A nozzle is preferably fitted into each spaced opening. The pattern die has material passages that communicate with the material passages in the die block for delivering the viscous material to the nozzles. The nozzles receive the viscous material from the material passages in the pattern die, and emit the material as spaced strands. The pattern die further includes a series of spaced air outlets that are also preferably aligned on a common axis along the lower surface of the pattern die. The pattern die air passages communicate with the air passages in the die block and provide pressurized air to the air outlets. Preferably, a pair of air outlets are positioned adjacent each material outlet and each air outlet is formed on an opposite side of the respective material outlet.
In operation, the pattern die emits the viscous material preferably from the nozzles as spaced strands toward a surface of the moving substrate. The pattern die also emits air generally between the strands to draw down and attenuate the strands into small fibers that are deposited uniformly onto the moving substrate.
The orientation of the material outlets and air outlets in accordance with the principles of the present invention preferably causes the fibers to oscillate in a generally cross-machine direction that improves blending of adjacent fibers. The air between the material outlets also prevent entanglement of adjacent strands during the critical draw down phase to reduce xe2x80x9cshotxe2x80x9d formation on the moving substrate. Additionally, the orientation of the material outlets and air outlets requires less volume and velocity of air to create a uniform pattern of fibrous on the web. With less volume and velocity of air, the material dispensing system reduces undesirable xe2x80x9cflyxe2x80x9d formation and lowers operational and maintenance costs of the material dispensing system. Moreover, the orientation and operation of the material outlets and air outlets improves the ability to modularize the dispensing system to provide a wider range of uniform pattern widths across a moving substrate.